The field of the invention is ear cushions for headphones, and particularly, methods of making contoured ear cushions from cellular materials.
Cellular materials have been used on headphones for many years. As disclosed in U.S. Pat. Nos. 3,593,341; 3,084,229; 2,622,159 and 3,586,794, such cushions are made from various types of cellular foam plastic materials. These materials vary in their cell density (i.e. pores per inch) and in their porosity. In high quality headphones intended for the high fidelity market, these variables are carefully chosen for their specific effects on the acoustical characteristics of the headphone. For example, a less porous material provides a greater sealing effect between the headphone and the ear which enhances the bass response of the headphone. On the other hand, more porous materials do not enhance the bass response, but they do provide a more open sensation which is desired by some users. It is the objective of the headphone manufacturer to select an ear cushion material which provides the desired acoustical properties and then to mass produce the ear cushion. The ear cushion must be economically produced in large numbers and its acoustical properties must be well controlled.
Ear cushions can be shaped in a variety of ways to enhance the seal with the ear and to improve user comfort. Although many shapes, or contours, are known in the art, only a relatively few contours are actually used in commercial headphone products. This is particularly true of ear cushions formed from porous plastic foam materials which are typically die cut into circular discs or circular rings. Attempts have been made to mold foam cushions by heating the material, but such methods take too much time or form a skin on the material which is acoustically undesirable. For example, a typical porous foam material may require as much as one hour in an oven before it can be molded into a cushion. Clearly, this is impractical for mass production and attempts to speed up the process by raising the temperature have destroyed the cellular structure or put a skin on the surface of the ear cushion. Neither result is desirable from an acoustical standpoint.